Although family, twin, and adoption studies indicate that heredity plays a role in manic-depression (MDI) and schizophrenia, the genetic factors involved or their mode of inheritance remains unknown. Important advances in molecular biology over the past decade now make it possible to determine the approximate chromosomal location of the gene(s) that may play a role in these illnesses. Toward this goal, identifying multigenerational families afflicted with MDI and schizophrenia is crucial. We have identified several such families and are searching for others. Permanent cell lines are being established and DNA processed for restriction endonuclease mapping. As a result of this project, the etiology, genetics, and treatment of MDI and schizophrenia may be better understood.